#include<iostream>
#include<vector>using namespace std;//判断是否有A>=B,
bool cmp(vector<int> &A,vector<int> &B)
{if(A.size()!=B.size()) return A.size()>B.size();for(int i=A.size()-1;i>=0;i--)if(A[i]!=B[i])return A[i]>B[i];return true;		} //C=A-B;vector<int> sub(vector<int> &A,vector<int> &B){vector<int> C;for(int i=0,t=0;i<A.size();i++){t=A[i]-t;if(i<B.size()) t-=B[i];C.push_back((t+10)%10);if(t<=0)t=1;else t=0;	}while(C.size()>1&& C.back()==0)C.pop_back();//去掉前导0；return C;}int main(){string a,b;vector<int>A,B;cin>>a>>b;//a="123456"for(int i=a.size()-1;i>=0;i--)A.push_back(a[i]-'0');//A={6,5,4,3,2,1}for(int i=b.size()-1;i>=0;i--)B.push_back(b[i]-'0');auto C=sub(A,B);for(int i=C.size()-1;i>=0;i--)cout<<C[i];return 0;}